The invention is in the field of marine propulsion mechanisms, and specifically pertains to submerged propeller drive mechanisms.
A typical ship's propeller is fairly inefficient. Whereas most of the forward thrust generated by the propeller is derived from the movement of the extremities of the propeller blades through the water, inasmuch as this region of the propeller is moving much faster than the rest, nonetheless the major portion of the blade structure is comprised of radially inner blade regions which do not generate nearly as much thrust as the extremities.
Because the entire length of the blade is used for thrust in most propellers, and because the pitch of the blade elements is dependent not only upon its speed, which in turn depends on its radial distance from its axis of rotation, but also the axial distance from the propeller's leading edge, the blade must be made in a fairly complex configuration with carefully controlled contours. This requirement causes blades to be rather expensive. This expense in creating the entire blade such that it strikes the water at every point at the optimal angle for delivering thrust may not be justified in view of the fact that the major portion of the blade delivers relatively little thrust. In other words, if only the outer perimeter were properly contoured and the inner blade portions were omitted entirely, not a lot of thrust would be lost.
Another built-in inefficiency of the conventional propeller lies in the fact of cavitation. As the blade rotates and thrusts water rearwardly, it is expelling water faster than water is being replenished from the front of the propeller, causing vacuums to exist in front and at the sides of the propeller. The fact of cavitation considerably decreases the efficiency and the effectiveness of conventional propellers. If cavitation could be reduced and even eliminated, the result would be a noticeable increase in power and efficiency.
There is a need, therefore, for a submersible propeller blade which operates on an annular portion of the periphery of the propeller rather than the entire circular area circumscribed by the rotating propeller, and that makes provision to avoid cavitation.